Typically, an ink jet printer has at least one printing cartridge from which droplets of ink are directed towards a receiver. Within the cartridge, the ink may be contained in a plurality of channels and energy pulses are used to cause the droplets of ink to be ejected on demand or continuously, from nozzles or orifices in a plate in an orifice structure.
In a thermal ink jet printer, the energy pulses are generally provided by a set of electrical resistors, each located in a respective one of the channels, each one of them is individually addressable by current pulses to instantaneously heat and form a droplet or bubble in the channels which contact the resistors. Operation of thermal ink jet printer is described in details in U.S. Pat. Nos. 4,849,774; 4,500,895; and 4,794,409.
On the other hand, a piezoelectric ink jet printing system includes a body of piezoelectric material defining a plurality of parallel open topped channels separated by walls. The walls have metal electrodes on opposite sides thereof to form shear mode actuators for causing droplets to expel from the channels. An orifice structure comprising at least one orifice plate defining the holes through which the ink droplets are ejected is bonded to the open end of the channels. The electrical energy pulses are applied to the parallel electrodes causing the channels to shear actuating the expulsion of droplets from the orifice plate. Operation of piezoelectric ink jet print heads is described in details in U.S. Pat. Nos. 5,598,196; 5,311,218; and 5,248,998.
Ink jet printing cartridges, whether it is of thermal or piezoelectric kind, use a variety of functional components, all of which must cooperate in a precise manner to achieve maximum efficiency. One of the most important components is an orifice plate having a plurality of orifices or nozzles therein. The nozzles are usually circular in cross section and the diameter of the nozzles may vary from 10 to 100 .mu.m as required by the specification of the printer. Higher the resolution of the printed output, smaller is the ink droplet thereby requiring smaller diameter nozzles or orifices. Ink is ejected through these openings during printing operation. To obtain defect-free printing output, the orifice plates and all the nozzles must be kept clean and free of debris and any kind of obstructions to ink flow at all times. If the orifice plate and nozzles are not clean, many problems can occur thereby undermining the performance of the printer. As for example, paper fibers and other debris accumulated on the orifice plate surface and inside the nozzles can affect the quality of the printed images. Similarly, debris can be dried ink crust and paper dust on the orifice plate as well as in the ink channels and the nozzles can cause the printer to perform poorly.
The foregoing problems are overcome, as described in U.S. Pat. No. 5,300,958 to Burke et al, by providing "maintenance or service stations" within the main printer unit. The maintenance stations are designed such that when the printhead ink cartridge is not operating and is in a "parked" position, the cartridge is situated in the maintenance station outside the printing zone for the purpose of routine cleaning of the cartridges. The maintenance station has many components, which are designed to serve many functions. These functions include: (a) priming the printhead cartridge, (b) capping the orifice plate and nozzles (orifices) therein when the printhead is not in operation, (c) wiping contaminants from the orifice plate, (d) preventing ink from drying out in the openings of the orifice plate, and (e) providing a receptacle for discarding the cleaned debris.
To accomplish this cleaning, the U.S. Pat. No. 5,103,244 discloses a structure in which a multi-blade wiper is used. The desired cleaning is performed by dragging a printhead (cartridge) across the selected wiper blade. The wiper mechanism also includes a plurality of resilient blades each having an octagonal shape and rotatable about an axis.
Another cleaning structure disclosed in U.S. Pat. No. 5,300,958, includes a printhead wiper unit consisting of a single or dual members positioned against each other to form a capillary pathway therebetween. The cartridge includes a compartment having an opening therethrough and an absorbent member impregnated with cleaning solution.
Still another cleaning structure is disclosed in U.S. Pat. No. 5,574,485 which includes use of a high frequency ultrasonic liquid wiper wherein a cleaning nozzle is confrontingly aligned but spaced from printhead nozzles. A cleaning solution is held within the cleaning nozzle by surface tension to form a meniscus and is caused to bulge toward into contact with the printhead nozzle face and form a bridge of cleaning solution therewith. In addition to dissolving ink the cleaning solution is ultrasonically excited by a piezoelectric material immediately upstream of the cleaning nozzle to provide a high frequency energized liquid wiper to facilitate cleaning of clogged nozzles without having physical contact with the printhead nozzle face.